text: const assert = require('../assert.js').for('DocumentType');
  
  const {parseHTML} = global[Symbol.for('linkedom')];
  
  const {document} = parseHTML('<!doctype html><html />');
  
  const {documentElement} = document;
  
  assert(documentElement.shadowRoot, null, 'no shadowRoot');
  
  const shadowRoot = documentElement.attachShadow({mode: 'open'});
  
  assert(documentElement.shadowRoot, shadowRoot, 'yes shadowRoot');
  
  try {
    documentElement.attachShadow({mode: 'open'});
    assert(true, false, 'double shadowRoot should not be possible');
  } catch (ok) {}
  
  
  